First, Make The Zucchini Cake

1. Preheat & Prep. To start, preheat oven temperature to 350 degrees F. Grease a 9×13 metal baking pan and set aside. 
2. Combine Dry Ingredients. In a medium bowl, combine gluten-free flour, baking powder, baking soda, cinnamon, nutmeg, and salt. Whisk to combine well and set aside. 
3. Combine Wet Ingredients. In a large mixing bowl, combine oil, brown sugar, granulated sugar, eggs, applesauce, and vanilla. Whisk until smooth. 
4. Add Dry Ingredients To Wet Ingredients and stir until almost fully combined, with just a few dry spots left. 
5. Mix In Zucchini. Add the grated zucchini and mix until the zucchini is evenly distributed. 
6. Bake. Transfer the batter to the prepared baking pan and smooth out the surface into an even layer (this will help the cake rise evenly!). Bake at 350 degrees for 40-45 minutes, or until a toothpick inserted in the center of the cake comes out clean with just a few moist crumbs. (While the cake is baking, I recommend browning the butter for the frosting. See below!) 
7. Cool Completely on a wire rack before frosting. (If you try to frost a warm cake, it will melt the frosting.) 

Make Frosting & Finish The Cake:

1. Brown Butter & Chill Till Solid. Melt the butter in a light-colored saucepan over medium heat, whisking constantly until the butter begins to foam. (Watch carefully when the butter begins to foam, as it will turn golden and brown quickly.) When the butter under the foam is golden (like honey) and smells sweet with a nutty aroma, remove the pan from the heat and let the butter cool for a few minutes before transferring to a large mixing bowl. (Make sure to get all those lovely brown bits!) Place the bowl in the refrigerator and chill until the butter has solidified again. 
2. Beat Butter. When you’re ready to make the frosting, remove the chilled brown butter from the fridge and beat with a hand mixer until it’s smooth and no longer stuck to the bottom of the bowl. (Pause as needed to scrape down the sides of the bowl) 
3. Beat In Cream Cheese. Add softened cream cheese to the butter and beat on medium speed 2-3 minutes, or until well blended and smooth. (You don’t want any lumps!) 
4. Finish Frosting. Scrape down the sides of the bowl and add powdered sugar, vanilla, and salt (if using). Mix on low speed 20-30 seconds, until small clusters form, then increase the speed to high and beat 2-3 minutes, or until the frosting is light, smooth, and even.
5. Frost Cooled Cake. Add frosting to the cooled zucchini cake and spread into an even layer.
6. Serve & Store. Cut cake into slices and enjoy right away or chill leftover cake 2-3 days. We recommend covering the cake well with plastic wrap or an airtight lid to keep the cake moist.